7604 Notices of New Books. 



inducement for their preservation and development ; and, secondly, 

 supposing they might have a small proportionate influence in the 

 course of natural selection, — that a line of development following the 

 formation of any more important organ would certainly obliterate it. 

 These objections Mr. Darwin meets by assuming that many function- 

 less organs may be either members in an incipient state of formation, 

 not yet fulfilling their allotted functions, or those that have passed out 

 of use and become aborted, and also as there is an evident relation in 

 the development of distinct parts of an organic structure (as in the 

 proportion of head to limbs before instanced) that the modification 

 and formation of some useful organ, by the active process of natural 

 selection, may, on the principle of correlation of growth, influence a 

 parallel but functionless development of some other part. 



The limited evidence of the formation of organs of great complexity, 

 as the eye, by natural selection, from parallel organs of simpler and 

 scarcely related structure, is another diflSculty ; but although the gra- 

 dated series of links connecting them is incomplete, Mr. Darwin says 

 that the possibility of its entire completeness is implied by the 

 existence of little isolated parts of the complete series gradating up- 

 wards in almost every point in the scale of animal organization ; that 

 the principle of extinction is accountable for the breaks in the series, 

 and, as soft organs cannot be preserved in a fossilized state, that the 

 geological eras might otherwise afford evidence of more complete 

 gradations. 



Highly remarkable special organs of unusual character, being com- 

 mon to two widely distinct genera — for instance, a peculiar arrangement 

 of the pollen-grains, similar in Orchis and Asclepias — would throw 

 doubt on community of structure being necessarily the result of blood 

 relationship ; but Mr. Darwin considers such cases as attributable to 

 natural selection working, in distinct courses towards a similar result, 

 for the good of the possessors, " in the same way as two men have 

 independently hit on the ver}' same invention." 



As a means of accounting for the formation of some complex organs 

 by the process of natural selection, Mr. Darwin supposes the possibility 

 of the transition of functions, i.e., that an organ may be developed to a 

 certain stage for a particular function, then perform some supplementary 

 function which may for a time accompany the normal function, and, 

 by gradual use, ultimately become the dominant and only function, 

 the use for which the organ in its early stage was constructed being 

 entirely obliterated. At page 210 (third edition), Mr. Darwin says : — 

 " The illustration of the swim-bladder in fishes is a good one, because 



